Tutorial 3
Q1.
A receiving system employs an antenna with a noise temperature of 40 K which is connected to
a parametric amplifier through a waveguide with 1.6 dB loss. The parametric amplifier has a gain of
16 dB and a noise temperature of 60 K. The amplified output is connected to a TWT amplifier with
a gain of 23 dB and a noise figure of 6 dB. The output of the TWT is connected to a mixer with a
noise figure of 13 dB. Calculate the effective noise temperature:
(a)
at the antenna terminals with the antenna disconnected'
(b)
at the input terminals of the parametric amplifier.
The standard temperature is 290 K.
Solution:
LO
T
a
=40 K
Feedline
L
1
=1.6 dB
Parametric
amplifier
G
2
=16 dB
T
2
=60 K
TWT
amplifier
G
3
=23 dB
F
3
=6 dB
Mixer
F
4
=13 dB
IF
Antenna
Feedline:
Loss
1
1.6 dB
1.4454
L
==
Gain
1
1
11
1.4454
G
L
Effective noise temperature
0
(1
)
(
1
.
4
4
5
4
1
)
2
9
0
1
2
9
.
2
K
TLT
= =

× =
.
Parametric amplifier:
2
16 dB
39.8
G
2
60 K
T
=
TWT amplifier:
3
23 dB
199.5
G
3
6 dB
3.98
F
330
)8
6
4
.
2
K
TFT
Mixer:
4
13 dB
19.95
F
440
)5
4
9
6
.
3
K
(a) Effective noise temperature
3
24
1
21
2
3
248.68 K
e
T
TT
GG
G
G
=+ +
+
=
.
(b) Total effective noise temperature of the system
288.68 K
sea
TTT
=+=
Let
e
T
′
be the equivalent effective noise temperature of the input of the parametric amplifier.
Then
1234
234
()
(
)
′
os
e
Nk
T
B
G
G
G
Gk
T
B
G
G
G
.
1
199.1 K
es
G
′
∴=
=
.
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View Full DocumentQ2.
A terrestrial microwave lineofsight radio relay link is required between two points 40 km
apart.
(a) If each parabolic antenna has a diameter of 2 m and an aperture efficiency of 50%, while the
operating noise figure of each receiving system is 13 dB, calculate the minimum carrier power
required for the transmission of colour TV. Assume that the bandwidth of colour TV to be 10 MHz,
and the signaltonoise ratio for good quality reception to be 40 dB.
(b) Given that the physical radius of the earth is 6400 km, calculate the height of the antenna above
ground (assuming the antennas are of the same height) for satisfactory operation at 4 GHz.
Solution:
(a) Given
0.075 m
λ=
.
2
2
m
42
ee
D
A
ππ
=η
=
.
2
4
3509
e
A
G
π
==
λ
.
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 Spring '11
 HuiHoonTat
 Amplifier, Decibel, Noise Figure, Parabolic antenna

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